Selenium nano particles (SeNPs) were prepared using fish gelatin dispersion system, and its particle size, morphology, and digestive stability were studied by dynamic light scattering (DLS) and scanning electron microscopy (SEM). The antioxidant capacity of SeNPs were determined. The results showed that fish gelatin was excellent dispersion system for preparation of SeNPs. The particle size of SeNPs and its morphology was barely affected by the concentration of fish gelatin dispersion system. Moreover, SeNPs presented good antioxidant ability. Among them, the DPPH radical scavenging ability of SeNPs prepared by 1.000%, 0.500%, 0.125% fish gelatin dispersion system, and IC50 value were 1.846 0, 0.923 0, ＜0.461 5 mg/mL, respectively. Correspondingly, the ABTS radical scavenging ability of SeNPs IC50 value were 0.580 0, 0.387 1, ＜0.193 5 mg/mL, respectively. It was found during the in vitro simulated digestion that gastric digestion would lead to agglomeration of SeNPs, and the agglomerated selenium particles regained nano-size during intestinal digestion.